These Are The Champions: 2018 US Open Series weekly recaps

The US Open Series features five weeks of the best hard-court tennis in the world on the road to Flushing Meadows. Check back each week to see who claimed glory in the lead-up to the US Open.

Week 3: Rogers Cup

The ATP and WTA World No.1s each made a statement to begin their summer hardcourt seasons, as Rafael Nadal and Simona Halep were each crowned champions north of the border in Canada at the Rogers Cup.

Halep defeated reigning US Open champion Sloane Stephens in a marathon, 7-6(6), 3-6, 6-4 final in two hours and 41 minutes, while Nadal ended the run of Greece's Stefanos Tsitsipas, 6-2, 7-6(4).

It was a rematch of this year's French Open final to begin championship Sunday in Montreal, and Halep authored another comeback to claim her third title of the season. In Paris, the Romanian rallied from a set and a break down to claim her first Grand Slam title over Stephens, and she needed to save a total of four set points en route to winning the opening set in this championship match.

With the win, the Romanian claimed her second career title in Montreal, having also won the title in 2016 over another American in Madison Keys.

The story of the week in Toronto was Tsitsipas, who had a career week despite having his 20th birthday celebrations dampened somewhat with a championship defeat. Greece's No.1 defeated four Top 10 players - French Open finalist Dominic Thiem, Wimbledon champion Novak Djokovic, defending champion Alexander Zverev and Wimbledon finalist Kevin Anderson - en route to his second career final, and first at Masters 1000 level.

The World No.1 proved too much for the breakout star, however, as he captured five of the first six games in the first 30 minutes of the match and hardly looked back from there. The young Greek did put up some late resistance after dropping serve to begin the second set, as he broke Nadal as he served for the match and even held a set point in the 11th game.

Nonetheless, Nadal navigated his way past the threat, and won five of the last six points in the tiebreak to secure his fifth title of 2018, and first off of clay courts. He also defeated Tsitsipas to win Barcelona earlier this year.

Week 2: Mubadala Silicon Valley Classic

Two players seeking their first career WTA title came through to the final in the first week of women's action on the road to the US Open, but only one could come away as the winner.

That proved to be fast-rising Romanian Mihaela Buzarnescu, who captured the trophy at the Mubadala Silicon Valley Classic with a 6-1, 6-0 win over Greece's Maria Sakkari.

Buzarnescu's rise through the WTA ranks has been the story of the past 12 months, as the Romanian was ranked well outside the world's Top 100 at this time last season at World No.142.

With her run to the title on the campus of San Jose State University, the 30-year-old is assured of making her Top 20 debut in the rankings on Monday, as she'll sit squarely at No.20.

Though both players were looking for their first WTA title on the California coast, the Romanian had the edge in experience in finals this season. She was contesting her third championship match of the season, having finished as runner-up at the first two, as the 23-year-old Greek woman was competing in her first-ever WTA final.

Greece's No.1, who upset Venus Williams in the quarterfinals and was two games away from defeat against another American in Danielle Collins in the semifinals, was unable to author another comeback in the championship.

Sakkari totaled 34 unforced errors over the course of the match, as the No.5 seed broke serve five times and never looked back after winning the first five games of the match.

Week 1: BB&T Atlanta Open

The BB&T Atlanta Open has long been John Isner's house, and at the close of the first week of the US Open Series, the American put his name alongside the game's greats.

In a rematch of the 2017 final, top-seeded Isner defeated No. 8 seed Ryan Harrison, 5-7, 6-3, 6-4, to claim his second title of 2018.

Atlanta has been Isner's most successful stop on the ATP Tour: he has now won five of his 14 career titles in the Georgia capital, and he has played in eight finals in Atlanta in his career. With the victory, the 33-year-old American joins Pete Sampras, Jimmy Connors, Andre Agassi and John McEnroe as American men to win a singles tournament at least five times.

Playing in his first event since losing a historic, but heartbreaking, Wimbledon semifinal, Isner's second straight title run in Atlanta unfolded as the inverse of a year ago. In 2017, the American did not drop a set en route to championship glory, including a win over Harrison in the final.

Twelve months later, however, the top seed was stretched to three sets in each of his last three matches against Mischa Zverev, Matt Ebden and Harrison.

The younger American beat Isner at his own game in the opening set, as Harrison dropped just five points on his own serve to claim a set lead in the pursuit of his second career title.

Harrison converted the lone break point he held in the first set en route to winning it, but that proved to be the only game the No. 8 seed won on return in the match.

Harrison went 0-for-4 on break-point chances in the second set, while Isner's serve got hot at the right time in the decider.

The top seed served eight of his 21 aces for the match in the final set, lost just five points on serve and never faced a break point. Conversely, the world No. 9 broke once in each of the second and third sets to rally his way to a victory in just under two hours.